Elephants’ Toothpaste A tower of foam emerges from a graduated cylinder

Purpose  To observe the rapid decomposition of hydrogen peroxide when treated with a catalyst

Demonstration  The hydrogen peroxide had a few drops of detergent in it  When potassium iodide KI was added it catalyzed the decomposition of the hydrogen peroxide  The oxygen gas bubbled causing the detergent to foam 2H 2 O 2 2H 2 O + O 2 bubble

Concepts 1.Decomposition Reactions 2.Peroxides 3.Gases

1.Decomposition Reactions  Any reaction of the general form  ABA+ B  In a decomposition reaction a single substance breaks into two or more substances  We say the original substance has “decomposed” which means it has broken apart

2.Peroxides  A compound which has an oxygen- oxygen bond  Hydrogen peroxide is a common peroxide  Chemical formula H 2 O 2  Chemical structure HOO H

3.Gases  Occupy much greater volume than the solid or liquid substances from which they are formed  Expand to fill or escape the container they are in  Will foam in the presence of a detergent as in this demonstration

Conclusions  Hydrogen peroxide decomposed to form oxygen gas and water when treated with a catalyst  When trapped in detergent, the oxygen gas bubbles expanded and a foaming tower was produced

Comments  Many different peroxides are known to exist  Benzoyl peroxide is a peroxide used in acne medication which released oxygen to kill facial bacteria